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By ChrisZ
#79669
So it's time to fix the seat switches on the 928S. I have the two sets of 4 way switches, and on the passenger seat the front switch works but the back one does not. It "tries", you can hear the motor try to engage on the rear lift "up" option but the seat recliner is out cold.

First step remove seat, which wasn't too bad once I got my 6mm Snap on 1/4 socket and tapped it on each bolt to seat it properly. Then with the seat up I was able to see that one of the front/back bearings is gone (checking with Rog to see if he has that part) but more importantly pulling the plug to the rear motor for seat recline allowed me to see a good 12 volts on the socket which means switch is "working". However when you plug the seat motor in, voltage drops to 2v. Which means voltage drop in the switch, makes sense.

Hooking a 12v battery up to the plug side allowed me to move the seat recliner back and forth without much effort, so the problem once again is high resistance in the switch. Time to take it apart?

Well.... Maybe not?

The problem I think is that Porsche put way too much current through these switches. The switch has to be haptic (user friendly) and deal with people pushing it hard, soft, etc. And it is driving a motor, which is the worst kind of inductive/reactive load. So the switch eventually fails.

Why not use relays? For the AC system I have a 20a relay under the hood that is switched by the little overloaded 2a relay in the climate box. That 20a relay then closes the magnetic load of the AC compressor clutch, removing the need to replace the dopey relay in the climate unit (it can close a 50ma load for the big relay forever). So what if we wire in a pair of relays for the seat back/forth?

I can see this: The two wires from the switch will supply either +12/gnd or gnd/+12 based on if the switch is commanding front or back recline. Have this switch two 20a DPST relays, each with a diode and the diodes in opposite directions. Thus when you command back, relay 1 closes and when you command front relay 2 closes. The relays are wired to the motor so that when 1 is closed the motor gets +12/gnd and when 2 is closed the motor gets gnd/+12.

Presto: No need to revamp the switch (it can switch the little load of the relay) and you can be assured that the motor will always get full power.

Thoughts? Before I build this myself is there a commercial relay product that does this? I could see it being used in a lot of places, windows, door locks, seats, all sorts of high current things.

Chris
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By Adamant1971
#79689
Yep same issue with the window switches, all that power going through the switch contacts causes them to get built up then not make a good connection.

Personally I have had good luck taking the seat switches apart and cleaning them and I always use a little di-electric grease when I reassemble them. Just watch those tiny ball bearings. :)

But yes relays would be the ultimate solution, then the switches will live a happier existence. All modern cars employ relays.
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By ChrisZ
#79719
Bad news, Roger does not have the bushing. Is there a substitute, I seem to recall something that would work.
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By ChrisZ
#82226
Took the switch apart and cleaned it up, Getting the little copper switches inside there out and in is a pain, but I can see where carbon and such render these things inoperable. I'm going to work on a proper relay solution.

In the meantime I found re-assembling the switch to be pretty easy. The key is to put some dielectric grease on each spring, put the spring in the holder, then put a dollop of grease on the end and press the ball on it. The ball will stay on the spring even sideways. Then after lining up the switch pivots put 2 Q tips between the round switch button and the square top of the switch, then press it on the bottom of the switch using pressure on the button (the q tips will keep the square top square and even). Works like a champ, even did my 944S seats just to do it.

Meantime car is fixed for SITM and the mistress will be able to adjust away :-)

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Panorama September 2021

great representation ~!